Stents are used to treat occlusions in body vessels. Stents can be grouped based on their method of deployment: balloon expandable or self-expandable. Normally a balloon expandable stent is radially compressed onto a non-compliant balloon. The balloon expandable stent has a high radial strength, but when compressed it remains in the compressed state. When the balloon is inflated, the stent radially expands and maintains its shape after the deflation of the balloon. Balloon expandable stents are advantageous because they can be easily deformed for use in locations of curvature or where side branch access is required. Balloon expandable stents can also produce a higher radial force than self-expandable stents during deployment due to the physician's ability to control the pressure applied to the dilatating balloon. Tailoring the applied radial force during deployment can aid vascular remodeling of a hardened atherosclerotic vessel.
Self-expanding stents are “shape set” to the shape desired once deployed in the vessel. They are then compressed and constrained into a delivery shape, usually by a concentric sleeve containing the stent. The stent is then delivered to the desired location and the sleeve is removed. Upon removal of the sleeve, the stent returns to its “shape set” shape.
In U.S. Pat. Nos. 5,855,597 and 6,162,245, Jayaraman teaches a stent with self-expanding ends and a balloon-expanding middle. The stent can be attached externally or internally to a polyester fabric or extruded polytetraflouroethylene (PTFE) graft. The stent can also be extruded such that the stent and extruded tubes are jointly extruded together. The stent can be the middle layer of an extruded tube. Further, the stent may or may not be welded together. The stent can be placed at equal distances to each other on the surface of the graft and then attached to the graft by any suitable mechanism such as using sutures or adhesives.
In U.S. Pat. No. 6,168,621, Vrba teaches a stent with a self-expanding part at each end of a balloon expanding part. The self-expanding part is made from a shape memory metal, such as nitinol, so as to enable self-expansion at body temperature upon release of the stent from its delivery catheter.
In U.S. Pat. No. 6,315,708, Salmon et al. teach a stent with self-expandable sections at both ends of a balloon expandable section. The stent can be formed from nitinol by having different heat treatments for the central, balloon-expandable section as compared to the end, self-expandable sections. The stent could also be formed by having stainless steel for the central section of the stent and welding on nitinol end sections.
Regardless of the type of stent used, vascular plaque (e.g., atherosclerotic plaque) can be dislodged from the vessel wall during stent placement. The thrombi can form emboli that occlude vessels, leading to severe trauma such as strokes. Accordingly, it is desired to produce a stent that minimizes the risk of emboli production and that can capture thrombi.
During minimally invasive percutaneous deployment procedures, stents are often guided through tortuously curved and complex vasculature. The final location of the stent can also be along a length of vessel that curves sharply. Accordingly, a stent having a flexible body which can contort to the curvature of a vasculature is needed.